1. Field of the Invention
The present invention relates to an automatic focusing device of a video camera capable of quick and accurate focusing.
2. Description of the Prior Art
Hitherto, various types of automatic focusing systems for a video camera have been known and one of them is an automatic focusing system of a television camera disclosed in Japanese Patent Examined Publication No. 5265/1964. In this system, the high frequency component is extracted, through a high-pass filter, from image signals obtained while the focusing lens is moved for focusing and when the level of the high frequency component arrives at its peak, the focusing is judged to be finished, thus the system is generally called "a mountain-climbing method".
In this "mountain-climbing method" as it is called, the detection of the peak level of the image signal may only be done immediately after the peak level while the focusing lens is moved. Therefore, even if the focusing lens is stopped concurrently with the detection of the peak level, the position of the lens is already ahead of the right position of focusing and the lens thereby needs to be moved back in the reverse direction. When the lens is moved back in the reverse direction as mentioned above, the right position of focusing is determined at the point of time when another arrival of the high frequency component of image signals at its peak level is detected. (Such phenomenon is called the hunting phenomenon.) In this case, the image screen becomes obscure.
Further, in the aforesaid "mountain-climbing method", the blurred image caused by an erroneous focusing can not be judged as it is blurred unless the motor for moving the focusing lens is driven, thus there is a possibility that the blurred image continues to appear when the subject is at a standstill.